Sterile neutrinos at the Neutrino Factory

IDS-NF plenary meetingOctober 19-21, 2011Arlington, VA, USA

Walter WinterUniversität Würzburg

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Contents

Motivation Steriles at near detectors Steriles at far detectors Simulation and general constraints Dependence on assumptions Summary

(mostly based on: Meloni, Tang, Winter, Phys.Rev. D82 (2010) 093008, arXiv:1007.2419)

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Motivation: eV2 sterile s

LSND/MiniBooNE antineutrinos Reactor anomaly

Global fits(a

rXiv

:100

7.11

50)

(B. F

lemin

g, TA

UP

2011)

(Kopp, Maltoni, Schwetz, 1103.4570)

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Arbitrary sterile s

Cosmology: upper bound O(1 eV) However: sterile neutrinos even preferred,

if light enough Cannot exclude

that light sterileneutrinos “hide“among the actives

(Hamann et al, Phys.Rev.Lett. 105 (2010) 181301)m1

m2

m3

m4 ?

Steriles at near detectors

… focus on 3+1 framework in the following (for the sake of simplicity)

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Oscillation physics

Can be described independent of parameterization (with mixing matrix only)

Probabilities for short baseline limit:

Observation:Appearance probabilities

depend on two mixing matrixentries, disappearance

probabilities on one

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Choice of parameterization

Why do I need a parameterization? Less parameters (unitarity assumed!) Convenient if long-baseline included (matter effects)

Requirements for a parameterization:

Our parameterization:

(Meloni, T

ang, W

inter, arXiv:1007.2419)

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Oscillation physics (2)

Parameterization dependent probabilities in short baseline limit:

For small mixing angles: qualitatively similar to param.-independent approach

(Melon

i, Tan

g, Win

ter, arXiv:1007.2419)

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Performance indicators

Discuss constraints for individual parameters (sensitivity limits for 14, 24, 34)

Requires marginalization over unknown other parameters

Renders appearance channels useless: always sensitive to a combination of mixing matrix elements/parameters

Main sensitivities: 14: Pee (difficult at NuFact)

24: P (leading at NuFact)

34: P (currently impossible)

Sterile at far detectors

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Oscillation physics

Peculiarity: NC matter effect (affects only active states)

Probabilities to 2nd order: 14 difficult at long baseline,24 easiest,

34 by P (discovery channel)?[but: high enough statistics

compared to h.o.t. in other channels?]

(Meloni, Tang, Winter, arXiv:1007.2419; Discovery channel: Donini et al., arXiv:0812.3703)

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Hierarchy dependence

Characterized rel. to mass eigenstate 1:

Case |m412| ~ |m31

2|: A+D: m3 and m4 on top of each other B+C: m3 and m4 different (m41

2 = - m312)

Easier to identify because of matter effects?

Simulation and general constraints

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Assumptions

IDS-NF baseline 1.0 (50 kt + 50 kt) Near detectors:

At d=2 km with 32 t each (far detector limit) Electron CID with 40% efficiency, 1% mis-ID NB: May in fact need

additional near-near detectors to control systematics in disapp-earance channels See my other talk(+ Giunti, Laveder, Winter, arXiv:0907.5487)

Also tested seperately: OPERA-inspired MECC at same distance, hadronic channels, 10 kt

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Generalized exclusion limits

… without any constraints on m412

(Meloni, Tang, Winter, arXiv:1007.2419)

From e

disppearanceFrom

disppearanceFrom LBL-

disppearance(higher order effect)

90% CL, 2 d.o.f.

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Hierarchy dependence

A+D: Sensitivity at |m41

2| ~ |m312|

destroyed (correlations)

(Meloni, Tang, Winter, arXiv:1007.2419)

Dependence on assumptions

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What special assumptions often made?

LSND-motivated m412

Fast oscillation averaged out at long L Special case m41

2 0 (MINOS, Adamson et al, arXiv:1003.0336)

Also no additional m412

See Meloni, Tang, Winter, arXiv:1007.2419

Two-flavor limits, e.g.

(corresponds to same formula in our parameterization with m2 = m41

2 , = 14)

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24-34 for LSND assump.

Now if fast oscillations average out, two-parameter combinations can be tested:(otherwise m41

2-marginalization would lead to vanishing sensitivity)

detection at longbaseline (P) addsonly little if magicbaseline included(higher statistics in P)

(Meloni, Tang, Winter, arXiv:1007.2419; Discovery channel: Donini et al., arXiv:0812.3703)

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Near detectors added

Impact of ND depends on assumptions: m41

2 very large:Oscillations in ND averaged out

m412 ~ 1 eV2:

ND sensitive to spectral signature

(Meloni, Tang, Winter, arXiv:1007.2419)

Curvefrom last

slide

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Comparison to MINOS

Also experimental collaborations use special assumptions, e.g. additional parameters fixed

Comparison to MINOS: Tremendous increase of sensitivity, especially for large 13

Is 3+N a physics case for the Neutrino Factory, even if 13 large?

(Meloni, Tang, Winter, arXiv:1007.2419; compared to MINOS, Adamson et al, arXiv:1003.0336)

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Summary and conclusions

Sterile neutrinos may have m412 ~ 1 eV2, but

could also hide among the activesTechnically challenging, therefore hardly

tested?

Neutrino factory can access some of the sterile parameters very well, even at the longer baselines m41

2 ~ 10-4 – 10-1 eV2

Precision physics case even for large 13?

So far, no physics case for found;perhaps additional phases for steriles?